Chewing gum has a tendency to get stale. Moisture is lost from the gum when the ambient relative humidity is less than the equilibrium relative humidity of the chewing gum composition. Under these conditions, the gum becomes stale and brittle.
Humectants are substances that promote the retention of moisture. Various humectants for chewing gum compositions have been disclosed. U.S. Pat. No. 4,166,134 discloses the use of sugar alcohols and U.S. Pat. No. 3,632,358 discloses the use of glycerin. U.S. Pat. No. 4,824,680 discloses an improved method to employ sorbitol as a humectant.
Invert sugar is a mixture of 50% glucose and 50% fructose made by the hydrolysis of sucrose. Sucrose is a disaccharide in which one molecule of .alpha.-D-glucose in the pyranose or six-membered ring form is condensed with one molecule of .beta.-D-fructose in the furanose or five-membered ring form through their respective acetal and ketal functions. Sucrose is nonreducing, and because of the unique carbonyl to carbonyl linkage has great acid lability. Sucrose also hydrolyzes readily in acid systems to form invert sugar. The term invert sugar is used because prior to the hydrolysis, in the starting sucrose solution, a plane of polarized light rotates to the right and in the inverted solution a plane of polarized light rotates to the left.
Sucrose may be hydrolyzed with strong mineral or weak organic acids, the enzyme Invertase, or ion exchange resins. Commercial invert sugar is produced by the inversion of 96% cane sugar solution. The inversion is done at pH 3 to 4 by means of Invertase and diluted hydrochloric acid. The acid is typically neutralized with sodium carbonate to pH 6.5. At this higher pH, the dextrose crystallizes and the entire mass is beaten into a creamy plastic product.
Invert sugar is primarily used in commercial operations as a crystallization inhibitor and a food plasticizer. Invert sugars which can have various levels of sucrose inversions, are sweeter than sucrose at comparable concentrations. This greater sweetness is due to the D-fructose (levulose) component of the syrup.
U.S. Pat. No. 4,271,199 suggests the use of 1 to 25% invert sugar to improve chewing gum flavor. However, it exemplifies the use of 17% invert sugar. Such a high level of invert sugar causes gum to retain too much moisture, making the gum sticky and sweaty and causing problems with packaging and consumer satisfaction. This problem is especially evident in climates where the relative humidity is routinely high and also during seasons when the relative humidity level increases.